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Old August 14th, 2012, 11:45 AM   #1
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Zoom Audio Sync issue - but not your normal kind

At my work we're having a strange audio sync issue with a zoom h4n, and was wondering what people think.

Googling the problem brings up a raft of sync issues related to either FCP or people with 5d's back when they recorded at exactly 24fps instead of 24.97.

But the problem we're having, has just popped up out of the blue. We've had no issues syncing our zoom to any camera, up until now.

We've tested it with an F3, EX3, and a 7d. The audio drifts out of sync from the zoom, in less than 20 secs.

We cant work out whats going on - the FCP settings are all correct. The F3, ex3 and 7d will all stay in sync. But the zoom drifts.

The only thing I can think of is that the internal quartz clock of the zoom has started to run slightly slow. But i've never heard of such a thing happening before.

Anyone have any ideas?
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Old August 14th, 2012, 12:11 PM   #2
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Re: Zoom Audio Sync issue - but not your normal kind

Does a test recording playback exactly in time when you play it back on the Zoom AND compared to playing the same track back elsewhere (like your computer, for example)? You may be right that the internal clock in the Zoom has gone out of spec.

Note that if the same clock is used for recording and playback in the Zoom (which seems likely) a recording will play back in proper length, but when played back on another device will be a different length.
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Old August 14th, 2012, 12:16 PM   #3
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Re: Zoom Audio Sync issue - but not your normal kind

Was the sample rate on the Zoom set to 44.1, instead of 48 kHz. (standard for video)
In some NLEs, that would cause it to drift outta sync very quickly.
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Old August 14th, 2012, 08:28 PM   #4
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Re: Zoom Audio Sync issue - but not your normal kind

I was going to create a fresh post but then I stumbled upon this one. It sounds as if I am experiencing a similar issue, Zoom H4N, Canon 5D MKII. Both are set to 48kHz/16 bit. Shooting the normal 1080 24p with the 5D MKII. Tried using Pluraleyes in FCP 7.2, loses sync pretty quickly. Luckily, this was a promo and I used all short takes so I was okay but have some more shoots coming up that the client has specifically requested that I use the 5D MKII for and I am nervous about using the Zoom again. Should I dump the Zoom and get whatever is newer and better? The sound on the Zoom is adequate and the features are pretty good. But it is making life with my 5D MKII not very fun.

One variable, the Zoom was resting on a concrete floor on a shoot I did in Copenhagen a couple of years ago and through my own klutziness, I knocked it over hard enough to crack the glass on the Zoom's display. But it seems to work, record and run fine. Wonder if that impact could have messed something up in the Zoom? Seems unlikely, it wasn't a very big impact but I guess it could be possible?

Trying to think what other variables there could be and why the Zoom would lose sync so quickly. After a 10 minute clip, I would estimate that the Zoom sound had slipped from the 5D MKII by about 5-6 frames. Weird because I have used non-sync other sources for years (Mini Disc and my DVX100A) and those two would hold sync within a frame for up to 20-30 minutes. And that was with moving media on both sides.

Any suggestions on a culprit? Canon and Zoom are definitely set for 48kHz and 16 bit, it sounds like a sample rate mismatch but it isn't.
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Old August 14th, 2012, 09:04 PM   #5
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Re: Zoom Audio Sync issue - but not your normal kind

If you find the zoom causing issues you should test another unit out. The cost of fixing the problem could be much more than the cost of a new unit.
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Old August 15th, 2012, 07:54 AM   #6
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Re: Zoom Audio Sync issue - but not your normal kind

I got to the bottom of it last night - it's one of those little final cut bugs.

Dan - might be the same issue for you.


Apparently, final cut doesnt like anything without a timecode - like audio from a zoom. So on import, it stamps it with a timecode. But it doesn't use the settings from your project - instead it reefers to the default sequence preset, in the audio / video preferences.

So for us, one of our machines, had a preset set to an ntsc frame rate. So even when working on a 25fps project, when we brought in zoom audio, final cut stamps that audio as 29.97 fps, and we got audio drift.

I made a copy of the audio file, changed the preset in preferences to a 25fps sequence, then brought the copied audio clip back into final cut. - no sync issue.

Crazy. So on the timeline i have 2 versions of the audio- both are the same file. But one had the incorrect timecode stamp, and is a different length. madness!

So, if your having sync issues - goto audio/ video settings from the menu at the top, select the sequence presets tab, and check which sequence has a tick next to it. You need to tick one that matches the fps of your project. Reimport your audio, and hopefully all should be well!

I've attached a PDF that I wrote for our editors at work, but you guys might find it useful?

So, at least i got to the bottom of it eventually!
Attached Files
File Type: pdf fixing audio sync.pdf (211.7 KB, 351 views)
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Old August 15th, 2012, 10:48 AM   #7
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Re: Zoom Audio Sync issue - but not your normal kind

So if you had done the proposed experiment to see if the track plays properly on the Zoom vs. on your computer, you would have discovered that it wasn't a Zoom problem at all.

Good old FCP. Dunno why Apple doesn't just give up the market after virtually committing suicide.
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Old August 15th, 2012, 11:27 AM   #8
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Re: Zoom Audio Sync issue - but not your normal kind

Interesting Gotcha. Of course this could be called operator error as well. Not sure this is the case for Dan but likely. Gotta make those Easy set ups work for you.
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